1. Field of the Invention
The present invention relates to adjustment of an image density in an image forming apparatus.
2. Description of the Related Art
In a multi-color image forming apparatus, color densities of formed images of respective colors have changed from target densities and the formed images tints may change over time. To address this problem, the image forming apparatus forms a test pattern, measures amounts of applied toners using an internally attached sensor, and adjusts various parameters to attain desired densities.
According to Japanese Patent Laid-Open No. 2007-189278, a method of adjusting density changes of secondary colors has been proposed. More specifically, Japanese Patent Laid-Open No. 2007-189278 has proposed a color tone adjustment apparatus, which outputs a test chart including secondary colors, reads the test chart using a reading unit to grasp density variations of the secondary colors, and adjusts parameters associated with densities. Note that the secondary color means a color formed by superposing two types of toners (for example, yellow and magenta toners) of different colors. A ternary color means a color formed by superposing three types of toners (for example, yellow, magenta, and cyan toners) of different colors. These colors will be collectively referred to as multinary colors hereinafter.
However, with the invention of Japanese Patent Laid-Open No. 2007-189278, the test pattern has to be formed on a printing medium so as to detect the density changes of the secondary colors. Also, the necessity of the density adjustment is visually judged by the user. That is, the user has to control a copying machine to execute a print operation periodically or at an arbitrary timing, and has to judge whether or not to require the density adjustment by checking an image printed on the printing medium.